Microphone



(No Model.)

' A. W. S. DAVIS.

MICROPHONE.

,699. Paten ned Mar. 30, 1897.

UNTTEE STATES PATENT EErcE,

ARTHUR IV. S. DAVIS, OF LOWELL, MASSACHUSETTS.

MICROPHONE.

SPECIFICATION forming part of Letters Patent No. 579,699, dated March30, 1897. Application filed April 30, 1896. Serial No. 589,772. (Nomodel.)

To all whom, it may concern.-

Be it known that I, ARTHUR W. S. DAVIS, of Lowell, in the county ofMiddleseX and State of Massachusetts, have invented certain new anduseful Improvements in Microphones, of which the following is adescription sufficiently full, clear, and exact to enable those skilledin the art to which it appertains or with which it is most nearlyconnected to make and use the same.

This invention has relation to that class of microphones or telephonetransmitters in which granulated carbon is placed between the electrodesbehind the diaphragm, the obj ect of the invention being to render thetransmitter more highly efficient for augmenting and transmitting thoseatmospheric soundwaves produced by the slightest sounds; to prevent thatdisagreeable buzzing and crackling sound which is not only annoying, butrenders speech less clear; to permit of the use of battery-currents ofhigher tension for overcoming the high resistance of a long line, and toimprove the transmitter in other ways, as shall be hereinafter setforth.

To these ends my invention consists of a microphone or transmitterpossessing the features and characteristics which I shall 110w proceedto describe with particularity, and set forth in the specificationhereto annexed, and then point out in the claims.

Reference is to be had to the annexed drawings and to the letters markedthereon, forming a part of this specification, the same lettersdesignating the same parts or features, as the case may be, whereverthey occur.

Of the drawings, Figure 1 shows in vertical longitudinal section oneform of microphone or transmitter in which my invention is embodied.Fig. 2 is a front view of the same with the mouthpiece, the front plate,and the diaphragm removed. Fig. 3 shows the annular resilient orcushioning ring and the granular carbon therein. Figs. 4 and 5 aresimilar views in vertical section, showing some of the parts illustratedin Fig. 1, the carbon plug being formed in the two views with bosses ofvarying depths.

In carrying out my invention I employ a cylindrical casing Ct, having anannular flange b, which is externally threaded to receive a front plateor cap 0. The cap has a central threaded aperture into which is screwedthe flaring mouthpiece cl. The metallic diaphragm e is mounted betweenthe cap and the front face of the flan ge b and is accessible tosound-waves through the aperture in the mouthpiece. Thus far thetransmitter is no different from those now in use. The casing isprovided with a central longitudinal cylindrical aperture 6 and atransverse groove f, the bottom walls 9 of which flare outwardly.

h is a fiat curved spring lying in the groove f and having its endspressed against the flaring walls g. It supports the button having themetallic support i, which has a rearward] yeXtending boltj passedthrough an aperture in said spring, there being a female thumbscrew 70,with which the threaded end of the said bolt j engages, so that thebutton may be adjusted longitudinally as desired.

The support is formed with a central cavity to receive a carbon block Z,which is rigidly secured therein with its face flush into the face ofthe button. Also secured to the said button is an annular ring orsupport m of any suitable non-conducting elastic mate rial, as felt,rubber, or their equivalents, into which is fitted a carbon plug n. Thesaid plug is wider than the chamber through the ring, but is formed witha boss to fit into said chamber. In the said chamber, between the carbonplate and the carbon button, I place a small quantity of granular carbon0. It will be observed that the ring insulates the plug from the buttonexcept through the granular carbon and the carbon block.

The carbon plug is readily removable and has a convex outer surfacewhich rests again st the diaphragm, but is loose relatively thereto.

For different circuits of varying resistances I use plugs with thickeror thinner bosses, as the case may be, and a smaller or larger quantityof granulated carbon. That is to say, when the microphone is employedfor longdistance circuits, where a current of high potential must beemployed, I use a plug with a large amount of granulated carbon, andwhen the circuit is short, so that a relatively weak current is used,the amount of granulated carbon is decreased, and a plug with arelatively thick boss is employed, as illustrated in Fig. 4. In this wayI prevent those crackling or sparking sounds so often heard intelephones when a current of high potential passes through the granularcarbon, and at the same time greatly augment the sounds to betransmitted, and also reducing the amount of granular carbon to be usedto a minimum.

\Vhen a current is passing through a mass of granular carbon, theelectricity seeks the path of least resistance. Hence it passes throughthose contiguous grains which are largest and repels the smaller grains,since it meets less resistance in taking such a course. This causesconsiderable sparking and crackling, which of course aifects thediaphragm in the receiver and is sometimes so loud as to prevent thehearing of sounds made by the voice, whereas by the employment of acarbon plug with a boss the granular carbon may be retained in compactshape, so that the current can pass through it in practically straightlines instead of zigzagging through the larger grains. The carbon plugalso intensilies the microphones effect, as will be well understood.

The granular carbon is confined within th cushion-ring between the plugand the sup port, which ring permits the diaphragm to move the plugagainst the said granular carbon with the proper pressure.

It will be observed that the plug is not so great in diameter as thecushion-ring, and has its shoulders resting upon but a portion of thelatter. By this arrangement but a portion of the ring is utilized as acushion, and the carbon plug in vibrating with the diaphragm does nothave to overcome the inertia of the particles of the entire cushion.

The button may be adjusted so as to impinge upon the diaphragm by thethumbscrew and is supported upon a yielding or spring backing, which isso mounted as to expand and contract under the influence of thermalchanges without affecting the adj ustment of the button.

The thumb-screw 7a rests against a strip 17, to which one end of thebattery-wire is connected, the other end of the wire being connectedwith the diaphragm, so that the current passes from the diaphragmthrough the carbon plug, the granular carbon, the carbon block, themetallic support, the tllllll'lb-SCI'GW, and the strip 19.

IV hat I claim isr 1. In a microphone, the combination with a casinghaving a central aperture and a transverse groove, and a diaphragm, of abutton,

an adjusting-screw for the button, and a curved flat spring lying in thegroove, for supporting the button.

2. In a microphone, the combination with a casing having a centralaperture and a transverse groove, and a diaphragm, of a curved fiatspring lying in the groove, an adj nstingserew, and a button heldagainst the spring by an adjusting-screw, said button comprising asupport, a cushioning insulating-ring thereon, granular carbon in thechamber in the ring, and a carbon plug resting against the diaphragm andextending into the ring.

3. In a microphone, the combination with a casing, and a diaphragm, ofan adj ustable metallic support in the casing, a cushioningring havingits interior chamber filled with granular carbon and being secured tothe support, a carbon plug in contact with the granular carbon and thediaphragm, means for adjusting the metallic support toward and from thediaphragm, and a spring inserted between the said support and thecasing.

4. In a microphone, the combination with a metallic diaphragm, and ametallic support in rear of the diaphragm, of a cushioninginsulating-ring on the front face of the sup port, loose granular carbonin the chamber in the ring, and a solid carbon plug bearing against thering and havinga boss extending into the chamber in the ring andengaging the loose granular carbon, said carbon plug having a convexouter face bearing loosely against the diaphragm.

5. In a microphone, the combination with a metallic diaphragm, ametallic support in rear of the diaphragm, a cushioning insulatingringsecured to said support, and a mass of loose granular carbon in thechamber in the ring, of a series of removable and interchangeable solidcarbon plugs, each having a plug of a thickness different from theothers, said plugs extending for different distances into the chamber,whereby the amount of loose carbon is varied, and each plug having ashoulder bearing against the cushioning-rin g, and a convex face bearingloosely against the diaphragm.

In testimony whereof I have signed my name to this specification, in thepresence of two subscribing witnesses, this 18th day of January, A. D.1896.

ARTHUR IV. S. DAVIS.

\Vitncsses:

ARTHUR W. CRossLnY, (J. O. SrEcI-IER.

ICC

